Mountain pine beetles (pictured here) have killed pine forests over more than 140,000 square miles in the western US, but warming winters can’t be blamed for the full extent of recent outbreaks in the region, a Dartmouth College and US Forest Service study finds. Credit Jeff Foott

Mild winters not fueling all pine beetle outbreaks in western United States

Dartmouth College

HANOVER, N.H. – Warming winters have allowed mountain pine beetle outbreaks in the coldest areas of the western United States, but milder winters can’t be blamed for the full extent of recent outbreaks in the region, a Dartmouth College and U.S. Forest Service study finds.

Milder winters have contributed to recent beetle outbreaks in Canada, but this is the first study to evaluate warmer winters as a factor permitting simultaneous outbreaks across the majority of its range in the western United States. In the last 15 years, bark beetles in the western U.S. have killed pine forests over more than 140,000 square miles (about the size of Montana), which exceeds the area killed by forest fires during the same years. Warming winters could be fueling these beetle epidemics, but large-scale tests have been limited and other explanations are possible, such as rising summer temperatures that accelerate beetle development and the legacy of forestry practices.

The findings appear in the journal Landscape Ecology. A PDF is available on request.

The researchers examined the long-term trend in minimum air temperatures across 23 ecoregions in western U.S. forests that have had bark beetle outbreaks and assessed whether increased beetle survival due to warming winters permitted the outbreaks. The results show the coldest winter night has warmed by about 4 degrees Celsius (7 degrees Fahrenheit) since 1960 across Western forests. “This amount of warming could be the difference between pests surviving in areas that were historically unfavorable and could permit more severe and prolonged pest outbreaks in regions where historical outbreaks were halted by more frequent cold bouts,” says first author Aaron Weed, a former postdoctoral researcher at Dartmouth and now an ecologist at the National Park Service.

Despite the trend for warming winters across western U.S. forests, not all beetle populations between 1997 and 2010 have responded to winter warming. In the 11 coldest ecoregions, winter temperatures lethal to the mountain pine beetle have become less frequent since the 1980s and beetle-caused tree mortality has increased significantly in these regions. But in the 12 warmer ecoregions, recent beetle epidemics cannot be attributed to warming winters because earlier winters were rarely cold enough to kill the beetles.

Although winter warming has been occurring across the western United States for decades, it has only permitted mountain pine beetle outbreaks in regions where winters historically killed more than 50 percent of the beetles — primarily in the Middle Rockies (Idaho, Montana and Wyoming), the Blue Mountains in eastern Oregon and northern Colorado. In these regions, winter temperatures during the 1980s were more likely than in recent years to drop below the lower lethal temperatures for mountain pine beetles. But in coastal and southern regions, winters dating back to 1980 were never cold enough to cause substantial beetle mortality. However, these warmer regions are undergoing sustained and, in some forests, increasing impacts from beetles. Other factors — such as warming temperatures that affect seasonal rhythms of beetle development and forestry practices that have influenced forest composition, primarily pine density and age in this case — are necessary to understand the broad extent of mountain pine beetle outbreaks across the western United States, the study finds.

We live in the middle of a bunch of evergreen trees in the Pacific Northwest and have had some difficulty with bark beetles infesting fir trees on our property. I attributed it to dryer than normal conditions which after a couple of years left the trees weakened and more vulnerable to these pests. We have had above average precipitation for the past couple of years and the trees that survived all seem to be doing fine again.

Worked for the USFS long ago and bark beetle infestations were associated with drought conditions by forest service staff then. The irony was marking crews sent out to mark infested trees for cutting were told, IIRC, that six or more pitch streamers meant the tree would die. However, the timber sale programs of the USFS tend to move more slowly than climate change. One crew leader I knew became curious when they noted that trees their crew had marked looked remarkably healthy by the time the area was finally harvested. Curious, the crew leader to an axe to the bark where the streamers had originated and found – no living pests. The trees had recovered from the infestation and were perfectly healthy once again. The response of the forest S.O. to this report was “mind your own business and mark what you are told to mark.”

I have a son in law who has been in the forestry business for 27 years. He has observed the same thing. Soil moisture is the most important factor in both infestations and re growth. Tree planting practices have recognized this for years … at least in the Great White North. (Well it’s actually starting to green up some where the snow has melted up along the foothills of the Canadian Rockies though there is still snow in the forecast for Easter weekend.)

Read up on “optical depth” of the atmosphere. The short, over simplified version is that the break-even altitude would vary slightly with changing concentrations of GHGs. Since the probability of an encounter between a photon that wants to leave and a molecule wantis it to hang around is determined by atmospheric density and composition, the entire luke warmist-AGW catastrophist argument comes down to whether the chemical composition of the atmosphere (the proportion of GHGs to the rest) is more of an influence than simple atmospheric density. Evidence from historical geology suggests that density is immensely more influential than chemistry.
The earth has experienced “catastrophes” in the past, the biggest being the extinction at the end of the Permian. If you look over the Geocarb III model,http://earth.geology.yale.edu/~ajs/2001/Feb/qn020100182.pdf
you will see that the level of CO2 at that time was comparable to the level at present. CO2 levels increase following the extinction and remain high through the Mesozoic. One under-explored possibility for the cause of the Permian extinction is a “perfect storm” situation where low atmospheric levels of CO2 could cut primary productivity (as in biological prdouctivity on a planetary scale) catastrophically. Combined with pergiglacial “icehouse” conditions, similar to the present, those conditions could lead to a major extinction without any external influences (e.g. asteroid impacts). Since we are in a highly comparable situation vis-a-vis climate and atmosphere right now, we should be worried, but not, I think, about “excess” CO2.

From the lack of numbers suggested I gather you are saying you don’t know and nobody else does either. Nothing measured in the troposphere; slightly shrinking ionosphere (inferred by reduced satellite orbital decay at altitude). But a 4 degree decrease of low extremes is significant, if true. Significant of what, I have no idea. –AGF

The numbers are all over the internet, IF you bother to read the available literature. You can also look up both Rayleigh optical depth and Napieran absorbance. There are various flavors of theory as well, so you will encounter some discussion as to which is correct. I just don’t feel like looking it up for you. Have fun.

But in coastal and southern regions, winters dating back to 1980 were never cold enough to cause substantial beetle mortality.
That is something that has long bothered me about the “warm winters are causing pine beetle outbreaks” theory. The southern interior of British Columbia has rarely been subjected to bitter cold over the last 50 years. The climate is dominated by Pacific, not arctic, air masses. And yet only in the last few decades is the lack of bitter cold supposed to have created a pine beetle outbreak.
The second problem is that pine beetle outbreaks have also occurred in western Alberta, which today is subject to far colder winters than the interior of B.C. has ever recorded. So if the cold used to protect the interior of B.C., why is not now protecting Alberta?

rabbit:
I worked in the lumber industry and had a lot of communication with the MNR. They explained while the winters had become warmer it was more the age of their biggest food supply, the Lodgepole pine. Our fire control success has lead to the demise of what is probably the biggest forest re-newer . . . fire. Because of this, the interior Lodgepole pines are living longer than in the past, making for very soft wood and an excellent food source for the pine beetle. It isn’t so much because it is slighly warmer, it is because we aren’t getting the sudden freezes in Oct/Nov which catch the beetle on the outside of the trunk. As the weather slowly cools, it buries itself deeper into the trunk as a defense mechanism against the cold.
In addition, my former boss, who has forgotten more about forests than I know, explained that in the interior BC there is an approximately 200 year disaster cycle, fire, disease,etc., which forces a regeneration of completely new growth. He told me the pine beetles were right on time.
Anyway, that’s the way it was explained to me. FYI, the MNR people were NOT rabid AGW people. Just look at the at Anthony’s oceans reference page and you’ll know why we had such a warm winter here in BC. After studying that page I’m not buying a Gross mountain ski pass for the 15/16 season. That money was pissed away this year.

Sorry, Mike,
You’re not understanding the mountain pine bark beetle.
They do not bore into wood, they burrow under the bark and turn up the tree, munching on the phloem and laying their eggs.
Equally, the beetles are not hanging around the outside of trees in November; by that time larval development is well underway, eggs having been laid in August. Most of their existence happens in a tree, even mating.
There are beetles that digest dead wood and there’s one called ips, who shows up after the pine beetle has ravaged the tree.

Mike H,
I’m glad to hear that MNR folks aren’t rabid CAGWers, but your comment raises more questions than it answers.
Did MNR explain to you that the total global warming for that period was only ≈0.7ºC? Do they really believe tha such a tiny change makes a difference to the beetles? The change in diurnal temperatures is a hundred times greater every day.
Or do they believe that regional warming was occurring? If so, do they understand that the U.S. was much warmer in the 1930’s?
No doubt they know far more than I do about forests. But if those are their explanations, they are not convincing.

@db, I think Mike and Rabbit were referring to the Pacific coast and the Southern Interior of BC, I live in the SI area of BC (fairly similar to the Spokane and the Walla Walla region as far as climate is concerned rain shadow semi desert between the coastal mountains and the Rockies). It has been markedly milder the past 5-7 years ( I do 2x a day obs for Environment Canada since the early 90’s) Your global temp reference is no doubt correct but regionally speaking there can be larger variances than 0.7C. (BTW I enjoy your comments on WUWT)

More or less west of the Great Plains, summer drought is an annual event. As well, this area is drought prone throughout history – a mega-drought during the 12th and 13th centuries is believed to been the main cause of the collapse of the Anasazi culture. Now, add in the criminal mismanagement of the federal forests in the west, and over time conditions develop that are primed for large bark beetle outbreaks. If you live in the US, your federal forest resources are being wasted, costing the American taxpayer billions.
But, the situation is worse if you happen to have the misfortune of living in a county dominated by a large National Forest. These counties have some of the highest poverty rates in the entire country, because the federal government has reneged on it’s implicit promise to return a portion of timber sale receipts to the counties. Now that Congress has failed to re-authorize the Secure Schools Act (=welfare instead of jobs from the forest), these counties are slowly wasting away. Which is what the progressive “elites” thousands of miles away want…
The first move to begin fixing what ails federal forests would be to repeal EAJA – the Equal Access to Justice Act, which has the unintended consequence of forcing the American taxpayer to fund the frivolous lawsuits again forest management on federal land. Then, and only then can we begin to address the problem of bark beetles in western, decadent, and dying forests.

We biked the Great Divide mountain bike route, and much of the worst pine beetle kills were in the colder higher areas, near 100% near Granby,Colorado “the icebox of the nation” The warmer forests of New Mexico were in much better shape.

“But in the 12 warmer ecoregions, recent beetle epidemics cannot be attributed to warming winters because earlier winters were rarely cold enough to kill the beetles.”
They meant to say “…winters were NEVER cold enough…”
It’s no surprise they cling to their failed hypothesis, even as they back-pedal; warmer winters were still responsible for (now reduced to ‘contributed to’) outbreaks in Canada even though something else caused them elsewhere. Certainty abides!
When I was burning beetles for the BC government in the 80’s, conventional wisdom was that the beetles would never fly more than 50 meters from where they emerged before entering their new home. The epidemic moved a good deal faster than that.
There were considerable resources invested in the fall and burn program and it was interesting that we always wound up returning to the areas we’d treated the previous year because we hadn’t eliminated the beetle. Meanwhile, enormous tracts of forest produced no evidence of them at all.
It was often the case that we incrementally took out every pine in certain areas, especially in mixed stands with spruce and poplar. It was my impression that, in the big pine forests, there was no endemic population being held in check by winter kill-off or some such fully understood natural force, but, rather, they just hadn’t discovered the smorgasbord yet and as soon as they did, they tucked in.

I remember reading some studies on the pine beetle several years ago that seemed to make sense. The pine beetle survives the cold temperatures by changing its body fluid to an anti-freeze in a process that takes time and is triggered by temperature. The study showed that the beetles could survive temperatures down to 30 degrees F below zero, but did not determine a lower bound. Most beetle mortality was due to either early cold snaps, before the beetle could sufficiently convert its body fluid for protection or late cold snaps after warmer conditions triggered the return to normal body fluid.

I’m no entomologist but I believe the anti-freeze phenomenon is common among insects and, indeed, plants,too.
With the lodgepole pine and white pine that I’m familiar with, the beetles always chose to enter the tree very low down, to the extent that, below the mossy duff, the flared root structure would be full of beetle galleries.
Obviously, in all winters, this would be a more protected spot than out in the open.
Fall and burn consisted of identifying infested trees, felling them, removing the snow from the base, scraping away the frozen duff down to mineral soil, piling bucked tree sections around the stump and burning it up. Lengths of the tree that were above galleries were not treated; it certainly seemed to be true that the trees were populated from the bottom up. Only occasionally was an entire tree full of beetles; like atomic orbitals, there was a preference to start on an adjacent tree before filling the one, even though it’s also apparent that beetles of a feather flock together.
When the big outbreak happened, even the branches were full of galleries and the pine beetle would be found in spruce that happened to be in the stand.

@mebbe, your observation about “anti-freeze” in plants is correct. As an ex fruit grower we are well aware of that. What we hate to see in our industry is a winter that has cold/warm spells repeatedly ( as in this past 14-15 winter) It weakens the antifreeze and we dread the chance of a cold snap through the March – April months because studies have shown that bud protection is very low by the end of January.

The warming winter argument always struck me as odd since the range of the pine beetle stretches down into Mexico, without the decimation of their food source. Apparently the beetles make little headway if the trees are young and healthy.

In the last 15 years, bark beetles in the western U.S. have killed pine forests over more than 140,000 square miles (about the size of Montana), which exceeds the area killed by forest fires during the same years.
(emphasis added)

The last time WUWT delved into mountain pine beetles and forest fires, it was triggered by a Joe Romm blog post which claimed 70,000 square miles. I looked into that figure and could not find any substantiation. Far from it, the cycle of references all seemed to lead to a 2011 US Forest Service report which claimed a total of 7 million acres in three states were affected by pine beetles, which translates into 10,938 square miles, or 28,328 square kilometers for the metrically-minded. Note the US Forest Service report said affected, which somehow got conflated into destroyed.
The earlier WUWT article is here. My comment (with references) is here .

10,000, 140,000, 1 .1 million square miles, who cares. Facts, figures, evidence, affected vs. destroys, established vs. speculation, all irrelevant.
The only important concern in the climate debate is that “humanity and their greenhouse gasses destroying forests” remains a talking point. You know like destroying the north and south poles, coast lines, polar bears and so on.
Speaking of polar bears makes me wonder why seals get short shrift, I mean why don’t they get their day in the spotlight as victims of humanities egregious behavior. And what about rabbits and beavers. They’re cute too. Not fair if you ask me.

With a bit of common sense the problem is obvious. Look at this graph of beetle spread below. The green line is 2006, the red line 2011. What you are seeing in the advance is the spread of an INFECTION. This is the pattern of how disease spreads, with clustering and break-outs. From infected population to healthy population.
The most obvious answer is that we are looking at an improved blue stain fungus. A mutation has taken place and those trees that are susceptible will be killed. The remaining trees, those individuals that are naturally most resistant will pass along this resistance to the next generation.https://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/cfs/assets/file/1550

@ ferd, thanks , nothing to do with temps, just one look tells me the infection and the MPB is spread by prevailing winds. And to me it is and has been a natural cycle for thousands of years . Cores taken from lakes in the Rockies have shown a pattern of MPB infestations followed by fires for centuries (btw Lodge Pole pine has a life of about 80-100 years I have been told that as earlier commenters have said, beetle attacks from the ground up and start in the older (weaker) trees first.

ferdberple,
I don’t think a new and improved fungus can explain it because you still need the vector to expand its range.
In the case of the MPB, it is pretty easy to quantify the presence of the beetle in an area, since the tree always produces pitch balls that you can see from meters away and count if you’re inclined.
I have done beetle probes and all you need is a thorough ocular survey.
Where I worked, no tree survived any successful beetle attack, even when apparently slight; they became chlorotic the following year and dead, the next. The fungus was already pretty potent!
There is absolutely no doubt that beetle numbers exploded and their range expanded.

I’ve long maintained that forestry practices have been to blame for much of the beetle kill in Colorado, which suffers from a largely monocultural body of aging trees, beginning with the Colorado gold rush in 1859, with many areas of trees crowded together because of too little human understanding and too much fire suppression. It’s gratifying to see this confirmed, even if they don’t think they’re specifically confirming it.

I’m not prompted to condemn forestry practices with such conviction.
Humans have not been doing significant forestry in BC for very long as compared to a single generation of trees, even short-lived ones such as lodgepole pine.
Although there was, I believe, a little bit of re-planting done on Vancouver Island in the 30’s, reforestation didn’t begin in the province until the 70’s. Those enormous expanses of nothing but pine are not monoculture; they reseeded themselves and other species probably couldn’t handle the short rotation of fire years. We consider lodgepole decadent at 100 years old but fire tends to be less patient. However, it tends to wait long enough to allow for a new seed crop. Beetles have no success with juvenile trees and also are not very fire-resistant.

I’ll add, too, that the human ability to initiate fire has been and continues to be much greater than our ability to control or extinguish it.
This was especially true before the advent of aerial tankers and helicopters. That’s not just because of their water capacity but also for the ability to discover remote fires and deploy personnel.

It is not just monoculture that may be impacting beetle growth rates. For many reasons, there has been a tremendous growth in the transportation of whole logs throughout BC and Alberta in the last 30-40 years. I am sure that whole colonies of pine beetles have been transported to fresh territories on logging trucks. Has anyone studied the infestation rates along highways and logging roads?

Craig,
It was a truism amongst beetle killers in my day that beetles traveled by truck just like regular people!
I’m sure that it has all been plotted by people that do that.
My first exposure to a massive outbreak after years of nibbling away at little colonies was an entire hillside suddenly destroyed one year. It was close to a sawmill town, so who knows?
I was contracted by the forests ministry to peel the bark off the stumps of every tree on that hill after the logs had been removed and convey it off-site to be incinerated.
It was insanity. I had dozens of people hunched over thousands of stumps chopping with axes and chisels.
Did I say, it was insanity?
Apparently, it wasn’t really effective.

Yes, I think you are on the right track here, although ferdberple may be onto something as well with his ideas about fungal mutation.
A ranger in RMNP told me long ago (mid-late 1980s) that – in his opinion at least – the MPB infestations were at least partially due to the MPB’s natural predators being affected by various human meddling,
In the natural world, when there is a sudden bounty of prey, many of the species that feed on this prey will increase their populations to take advantage of this resource.
Birds, for example, can raise additional broods in a nesting season if there is an abundance of food available to them. Beyond woodpeckers, there are additional potential predators/parasites of the MPB, including checkered beetles (Cleridae), fungi, bacteria, and wasps, but many of these hosts may rely on woodpeckers to more-or-less clear the way for them by exposing the MPB in the course of stripping away bark.
There are at least three resident species of woodpeckers in the Colorado Rockies:Hairy, Downy, and Three-toed, along with sapsuckers, and flickers, that are potential avian predators of the MPB.
Checkered Beatles:

This is a very effective technique for controlling bark beetles due to the voracious appetite of many Clerid species.

I live in the southwest in one such forest. One thing I have noticed over the years is the more densely populated an area is with trees, the worse the beetle damage, with ALL areas Ive found with wider spacing having at worst only minor damage that isn’t killing trees. There is also the fact human actions have hindered the forest fires that used to routinely clear out the younger trees here, point being that your average spot used to burn every 7-15 years according to some sources. Not very hot fires, many trees would survive, or be by passed entirely. Older trees here show these fire marks. So previously the density of the trees was lower, which would mean stronger trees more impervious to the beetles. I have old pictures taken from all over the area, which also suggest thinner density of treestands was the norm in the past. I also see outbreaks of them at both very high elevations and very low which suggest to me temp isnt the major factor in the beetles dominance. Also some of the spots I know with thinner density and no issues are at the lower elevations of the forests range where it is warmer.

How odd that ‘nature lovers’ hate the fact that ‘nature eats nature’. They hate the Uroboros.
They talk about ‘wholeness’ yet only see fragmentation.
They fail to understand that the patterns we see — the forms — unity — emerge from opposing spirals.
See my painting: The Flower Sermonhttp://www.maxphoton.com/flower-sermon/

Actually Rabbit central and northern BC has had temperatures of 50f below and extended periods around 40f below. These temperatures have been rare though for about the last 15 years and early cold freezes which also kill off the bugs has also been rare. PDO?.
This is the area where I live.

Cold was more prevalent in northern BC in the early part of the 20th century and latter part of the 19th century. The diaries of the explorers in the mid to late 1800’s are interesting. You can also download in the order of 75 to 100 years of records from Environment Canada for some places in the middle of BC (“North” to most lower mainlanders) to the Yukon. I have some archived on my computer but not on this phone thingy.

How far can a bark beetle fly? At least 2 miles, supposedly: http://cals.arizona.edu/extension/fh/bb_faq.html#5
Accordingly their spread should take human transport into account, by loggers and firewood collectors, and this should be added to artificial old growth due to fire suppression. Temperature must be a minor factor. –AGF

” Prior to European settlement, northern Arizona’s Ponderosa pine stands had 20 to 40 trees per acre. Today, many areas of northern Arizona have 800 to 1,200 trees per acre. This is a much greater density than can be supported under our climatic conditions. The bark beetles are simply one of the natural checks and balances that are regulating forest density.” (Ibid.)

Beetle killed pine trees do burn better than green (uninfested) pine. In 2014 in B.C. on the west side of the Rocky Mountains, the largest fire in over 100 years occurred burning over 250,000 ha all of which was in beetle killed pine. Beetle killed trees that have been dead for 5 or more years are drier, have more fine fuels, burn with a higher fire intensity and through more sparks further than green stands. I and my compatriots in the fire control and research community can only shake our heads at this report.

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